The present invention concerns improved semi-automatic fire arms, in particular the gas aperture systems of such guns.
It is known that in gas aperture or gas inlet mechanisms, part of the propulsion gases of the cartridge is diverted from the barrel of the arm through an opening called a gas aperture towards a cylinder/piston unit.
This piston moves in cylinder due to the pressure of the gases and exerts a thrust on a sleeve equipped with one or several rods which send the whole of the moving parts backwards so as to carry out the different ejection functions of the fired case, the recock of the firing system as well as the feeding of a subsequent cartridge to the barrel block.
The above-mentioned system contains a return spring which acts on the piston in order to re-position the piston.